Physics / mechanism
Proton Exchange Membrane (PEM) electrolysers split water via electrochemistry: at the anode, oxidation produces O₂ and H⁺ ions; protons migrate through a solid polymer membrane (typically Nafion) to the cathode, where reduction yields H₂. No liquid electrolyte — the membrane itself conducts protons. Key parameters: current density (1–3 A/cm² commercial, >4 A/cm² R&D), cell voltage (~1.8–2.1 V operating vs. 1.23 V thermodynamic minimum), stack efficiency (65–75% LHV), and membrane durability (target >80,000 hrs). Catalysts are Pt-group metals — iridium at the anode is the critical cost/supply bottleneck. Leading stacks: Nel, ITM Power, Cummins (Hydrogenics), Siemens Energy, Plug Power.
Competitive landscape
Alkaline electrolysis (AEL) is the incumbent — cheaper capex, no PGM dependency, but lower current density and slower dynamic response. Anion Exchange Membrane (AEM) electrolysis targets PEM performance without iridium; still pre-commercial. Solid Oxide Electrolysis (SOEC) achieves higher efficiency at 700–900°C, suited to industrial heat integration. SOEC from Topsoe and Bloom Energy targets baseload industrial hydrogen.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.